I have previously disclosed a filter assembly in the shape of a cylinder in which the filter element is a cloth mounted in a circular rim which can be rotated continuously. The filter element divides the cylinder into two chambers, each of which contains a small sector which is essentially sealed off from the chamber so far as transfers of liquids therebetween is concerned. However, the solids collected on the filter are carried by the filter element during its rotation into the sector through which a backwash fluid is transferred in a direction opposite to that of the flow of the mother liquor through the two chambers and the filter element. The backwash fluid removes the solid from the filter element, thereby cleaning it so that when the cleaned portion leaves the sector it is ready for removal of further solid from further mother liquor.
A major problem with this prior device is that fluid from the chamber tends to enter the sector with the solid, if the pressure in the chamber is greater than that in the sector. Conversely, if the pressure is greater in the sector than in the chamber, fluid tends to flow from the sector into the chamber, carrying with it solid matter which should be leaving the sector through a port connecting the sector with a sump.
A second problem experienced has been the fact that where there is a mixture of solids of various particle sizes, the use of a filter element of fine enough pore size to remove the smallest particles results in an extremely low rate of filtration. Conversely, if the filter element is of larger pore size, then the low end of the range of particles will penetrate the filter and enter the filtrate.
As is evident, it would be desirable that the system be modified so that the problem of fluid flow between the sector and the chamber be minimized and so that fine particle sizes could be removed from the mother liquor at a relatively high rate of filtration.